1. Field of the Invention
The present invention relates to automatic door operators, and more specifically to improvements in the control of automatic door operators.
2. Description of the Related Art
Three different types of automatic door operators with single-action cylinders are disclosed in U.S. Pat. Nos. 3,244,415 and 3,291,003 to Lunenschloss, et al. These include the swing operator which returns to the same position whether the door is opened or closed, the over-center operator which is used to open and close a sliding door and which pivots sidewardly with the door, and the inertia operator which also is used with sliding doors and which interacts with a door only when the door is near its open or closed position. These three door operators as disclosed are controlled by either the pneumatic circuit control system or the electrically operated pneumatic control system. With both systems, the speed at which the door opens and closes may be adjusted to be faster or slower, however, the opening and closing speeds are not adjusted independently from one another. In some applications, it is desirable that a door close more slowly than it opens.
U.S. Pat. No. 3,936,977 to Runft, et al. and U.S. Pat. No. 3,921,335 to Hewitt, et al. disclose door operators with double-acting cylinders which can be used to cause the door to open and close at varying speeds.